The present invention relates to a heating device for heating an advancing yarn in a texturing machine or the like.
Such heating devices are used in particular for crimping synthetic yarns in a false twist texturing machine, through which the yarn advances and is crimped. In so doing, the yarn advances in a heating channel, which is heated on its walls to a surface temperature that is above the melt point of the yarn. To this end, the heating channel contains a plurality of yarn guides, which guide the yarn at a distance from the walls of the heating channel. The yarn guides may be arranged on a support, which is exchangeably arranged in the heating channel. A heating device of this kind is disclosed, for example, in EP 0 731 197 and corresponding U.S. Pat. No. 5,628,176.
To set a twist previously imparted to the yarn, a heat treatment is needed, which covers the entire yarn cross section, so that in the known heating device, each yarn is guided in a separate heating channel. This ensures that in the case of multifilament yarns, each of the filaments receives an intensive heat treatment for crimping. The known heating device is unsuitable for the heat treatment of a plurality of parallel advancing yarns.
DE 196 50 677 discloses a heating device, which is used for heating a group of advancing yarns. In this process, the group of yarns advances in a heating channel in a yarn advancing plane parallel to the side walls of the heating channel. Such arrangements are unsuitable for use in texturing machines, inasmuch as they do not permit uniform heat treatment for crimping the individual yarns because of heat losses, in particular toward the edge of the group of yarns.
EP 0 905 295 discloses a heating apparatus for heating an advancing yarn, wherein the yarns are guided in a yarn advancing plane, which extends in spaced relationship with a heated wall. However, the publication provides no indication of how the yarn path can be stabilized, so that the yarn undergoes a uniform temperature treatment.
It is accordingly an object of the invention to further develop a heating device of the initially described kind such that one or more yarns advancing side by side receive a uniform heat treatment.
The above and other objects and advantages of the invention are achieved by the present invention and wherein an arrangement of the yarn guides within the heating channel is selected such that they form a plurality of yarn guide tracks extending side by side for guiding a plurality of yarns, and wherein the yarns advance at a predetermined distance from the channel bottom wall. A special advantage of the invention lies in that, regardless whether one or more yarns advance in the heating device, the yarns advance substantially at the same distance from the bottom wall. The plane of the advancing yarns as well as the distance from the bottom wall are selected such that substantially the same heating times, heating intensities, and frictions are effective on each individual yarn.
To obtain a stable yarn path in the heating channel with the least possible contact and, thus, the least possible looping friction, the yarn guides are arranged relative to one another such that zigzag yarn guide tracks form, in which the yarns advance.
The invention has the special advantage that when a plurality of parallel extending yarns advance through a heating channel, each of the yarns is subjected to a substantially identical ambient temperature. With that, there also exists the possibility of operating the heating device either with one yarn or with a plurality of yarns.
According to a preferred embodiment of the invention, the yarn path plane formed by the yarn guides, in which the yarns advance, extends substantially parallel to the bottom wall of the channel. As a result, the yarns advance at a constant distance from the heating channel, so that a particularly uniform temperature influence on the yarns is realized. Because of the unilateral opening of the heating channel, which is closed in operation by a cover, a temperature gradient develops between the channel bottom wall and the cover side of the heating channel. Inside the channel, the yarns advance at one level within the channel, so that temperature gradients in the heating channel exert no influence on the tempering of the yarns.
In this connection, the arrangement of a particularly preferred further development of the invention results in that a very uniform treatment of the yarns within the heating channel. To this end, the number and the arrangement of the yarn guides are selected such that adjacent yarn guide tracks have between each other a distance which remains substantially unchanged in the longitudinal direction of the heater.
Another development of the invention is used preferably in texturing machines, wherein two yarns are combined to one yarn upstream of the takeup. In this type of plying, it is often desired to have different heat treatments for the individual yarns, so that different types of yarn guide tracks are realized in a simple manner.
To ensure that the support inserted into the heating channel and the yarn guides arranged thereon permit heating the yarns as unimpeded as possible, it is preferred to make the support of a thermally conductive material. In this instance, the yarn guides are made of a ceramic or coated with ceramic, so that they exhibit a high resistance to wear. This results in particular in a long service life of the yarn guides. Furthermore, ceramic has the property that it decreases the tendency as exists in the case of conventional steel yarn guides, namely to accumulate inorganic components of the yarn, and that it shows less wear.
In a particularly preferred development of the invention, the support consists of a highly heat conductive material and is designed and constructed as a profiled rail which is shaped to define a plurality of parallel extending guide channels. The external profiled walls of the profiled rail are mounted to the walls of the heating channel. This arrangement realizes a very stable yarn path in the heating channel. In this connection, there exists even the possibility that the guide channels define the yarn guide track, and that thus the yarn advances directly in the rail.
To be able to realize a zigzag yarn guide track, it is possible to mold the yarn guides to the profiled rail. However, it is also possible to insert a plurality of ceramic yarn guides into each of the guide channels of the profiled rail. In this instance, recesses in the heating rail make it possible to produce holding means for such yarn guides in a simple manner.
It is preferred to design and construct the yarn guides with an L-shaped yarn guide edge, so that the spacings between the yarn and the side walls of the heating channel, as well as between the yarn and the bottom wall of the heating channel are defined by the yarn guide edge. Likewise, this measure leads to an equalization of the temperature treatment of the yarn within the heating channel.
In a particularly advantageous further development of the invention, the profiled rail is formed by a plurality of U-shaped individual rails. The individual rails are connected along their opposite longitudinal sides, so that no heat blockade develops between the individual yarn guide tracks.